Cleaned up axi library.
Changed payload size to be in host byte order by restricting size
of the first instance of the concatenation to be (1|2|4|8) B.
Got rid of word axi by talking about a GPIO map instead.
Renamed zdx tags into udx ones and piconf zynq into piconf zed.

Since GPIO mapping was never Zynq/AXI specific
it should work with MicroBlaze/PLB, too.
Fixed last commit by adding renamed files.